LEE COUNTY, Florida -- An FBI Task Force is now investigating a couple accused of taking photos and videos of themselves in sex acts with a 4-year-old girl from Polk County.

The FBI Innocent Images Task Force says the investigation could eventually come with state and federal charges for Alan Johnson and Jennifer Sparks.

A federal indictment has been obtained for the Production and Possession of Child Pornography. The indictment says Johnson and Sparks began capturing photos and videos with the young girl on May 12 of this year, though it could have started earlier. It continued through June 27.

Sparks and Johnson were arraigned in court on Monday. They didn't attend the hearing, but their attorneys pleaded not guilty to the six charges they're each facing.

Among those charges: Traveling or trying to travel to meet a child after using a computer to lure a child's guardian. Authorities have not revealed whether that guardian has faced charges.

Experts say for alleged sex offenders, it can start with cognitive distortion, being unable to properly deal with social cues.

"They're physically attracted to children, and they go through a grooming, courting process," says Wesley Jennings, an assistant professor in USF's Department of Criminology. "They think it's natural and normal to say hello to a child, then give them a high five the next day, then bring them ice cream the next day. They think they're involved in an actual courting process, a relationship."

Johnson is a registered sex offender who's been convicted on child porn charges before. Court documents say in 2003, he posed as a teenage girl online and sent photos, some showing girls under the age of seven.

After nearly six years behind bars, he was released, just a short time before these new accusations surfaced. Sex offenders can be triggered to re-offend, according to Professor Jennings, even if they've served time and are under community supervision.

"He may, for instance, be at home, not having a plan at all to look for another victim. But he may be sitting there watching TV. All of a sudden, he might pick up child pornography, so that's a precursor event," Jennings says. "Now he's initiated that re-offense cycle. And after he looks at this child pornography, he may go to, say, a movie theatre or a toy store or go to an ice cream parlor. Now he's placing himself in the environment with a potential victim."

The next court date for Johnson and Sparks has been scheduled for September.